<PAGE>
 
                                                                      Exhibit 11

                                   CORE, INC.

                     COMPUTATION OF INCOME PER COMMON SHARE

<TABLE>
<CAPTION>
                                    FOR THREE MONTHS ENDED JUNE 30,       FOR THE SIX MONTHS ENDED JUNE 30,
                                          1996       1997                         1996        1997         
                                   ------------------------------------------------------------------------ 
<S>                                 <C>           <C>                      <C>            <C>
PRIMARY:
Average shares outstanding          4,840,000    7,231,000                     4,840,000        7,214,000
                                                
Shares issuable on assumed                      
 exercise of dilutive                           
 options and warrants -                         
 based on treasury stock                        
 method using average                           
 market price                         901,000      550,000                       901,000          583,000 
                                   ------------------------------------------------------------------------
Totals                              5,741,000    7,781,000                     5,741,000        7,797,000
                                   ========================================================================
Net income                         $  499,082   $  683,330                    $1,036,766       $  823,401
                                   ========================================================================
Net income per common share        $     0.09   $     0.09                    $     0.18       $     0.11
                                   ========================================================================
<CAPTION>                                    
                                    FOR THREE MONTHS ENDED JUNE 30,       FOR THE SIX MONTHS ENDED JUNE 30,
                                          1996       1997                         1996        1997         
                                   ------------------------------------------------------------------------ 
<S>                                 <C>           <C>                      <C>            <C>
FULLY DILUTED: 
Average shares outstanding          4,840,000    7,231,000                     4,840,000        7,214,000
                                   
Shares issuable on assumed         
 exercise of dilutive              
 options and warrants -            
 based on the treasury               
 stock method using the            
 ending market price                  901,000      656,000                       901,000          636,000 
                                   ------------------------------------------------------------------------ 
Totals                              5,741,000    7,887,000                     5,741,000        7,850,000
                                   ========================================================================
                                   
Net income                         $  499,082   $  683,330                    $1,036,766       $  823,401
                                   ========================================================================
Net income per common share        $     0.09   $     0.09                    $     0.18       $     0.10
                                   ========================================================================
 </TABLE>